Photolithographic master and method of manufacture



April 30, 1968 F. o. BACH 3,380,824

PHOTOLITHOGRAPHIC MASTER AND METHOD OF' MANUFACTURE Filed May 12, 1964 FIG.

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United States Patent O 3,380,824 PHOTQLITHGGRAPHIC MASTER AND METHOD F MNUFACTURE Frederich 0. Bach, Villa Park, Ill., assigner to A. B. Dick Company, Niles, lll., a corporation of Illinois Filed May 12, 1964, Ser. No. 366,826 3 Claims. (Cl. 96-33) This invention relates to the art of photolithography and particularly to the production of a new and improved photolithographic plate and method for the preparation of same.

The term photolithography relates to the art of imaging a lithographic plate from an original by photographic technique. For this purpose, use is made of a base sheet having a water insoluble, water receptive, ink repellent lithographie surface coated with a material which reacts, upon exposure to light, to produce an ink receptive, water repellent imaged portion in the exposed areas whereby, when the plate is exposed to the original or to a transparent negative thereof, the exposed portions of the plate become ink receptive and water repellent and While the unexposed portions remain ink repellent and water receptive. As a result, when the imaged plate is Wet by aqueous medium or repellent and then by ink, water is retained by the non-imaged portions, leaving the imaged portions free to accept ink composition for transfer directly to copy paper or for transfer indirectly to the copy paper through the medium of an offset blanket,

To the present, such photolithographic plates have been made available in various modifications. in one modification, represented by the Mullen patent No. 2,693,145, use is made of a paper base sheet having multiple coatings formulated of an insolubilized hydrophilic colloid, such as casein, which provides the insolubilized, Water receptive, ink repellent, lithographie surface which is overcoated with a light sensitive bichromated gelatin which reacts upon exposure to light to convert the exposed areas of the colloid coating to an ink receptive, Water repellent irnaged portion, vWhile the colloid coating in the unexposed areas is removed by the repellent to expose the underlying lithographic surface which comprises the non-imaged portions of the plate.

Such multiple coated paper plates are relatively difficult to manufacture and they are expensive. The coated paper plate has a great tendency to absorb moisture to permit stretching, image distortion, curling and other undesirable performances in the plate.

in a later modification, such photolithographic plates have been fabricated of a coated, treated or hydrolyzed cellulose acetate alone or laminated onto a suitable base sheet, such as metal or paper, and wherein the hydrolyzed or treated cellulose acetate constitutes the water insoluble, water receptive, ink repellent lithographie surface. The surface is coated with a light sensitive diazo compound which converts to an ink receptive, water repellent imaging material upon exposure to light to produce the imaged photolithographie plate. Suitable diazo or diazo resin forming compounds for use as a light sensitive coating on a lithographie surface are defined in the Jewett et al. Patent No. 2,714,066.

The difficulty with such diazo sensitized, hydrolyzed cellulose acetate plates resides in the number of treatments and in the length of the treatments required to render the surfaces of the plate water Wettable. The instability of the sensitized plate introduces an aging problem in the use of the plate. In additon, the plate is still subject to the stretching and distortions when fabricated with a paper base sheet.

The difficulties of stretching and distortion are eliminated by the use of a metal base sheet, such as aluminum, as described in the Jewett et al. patent aforementioned,

wherein the surface of the aluminum plate is first treated with an aqueous silicate solution to stabilize the lithographic surface of the plate whereby the light sensitive diazo compound applied to the surface of the plate is stabilized to prevent deterioration and whereby the sensiiized plate is capable of being stored over relatively long periods of time without loss in the sensitivity of the plate.

Such diazo coated aluminum plates nd excellent use as a photolithographic plate but the cost of the aluminum sheet makes the plate relatively expensive for use where a limited number of copies are required to be produced.

It is an object of this invention to produce and to provide a method for producing a new and improved photolithographie plate.

More specifically, it is an object of this invention to produce a low cost photolithographic plate which is characterized by good dimensional stability, which has good aging characteristics, which is not subject to wrinkling or curling, which has good sensitivity to produce an imaged l lithographie plate upon exposure to an original or a negative, and from which a large number of copies of good quality can be produced by conventional lithographie printing techniques.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing, in which- FIG. l is a perspective View partially in section of a lithographie plate embodying the features of this invention;

FIG. 2 is a perspective view partially in section of the lithographie plate illustrated in FIG. 1 coated with a diazo compound to render the plate photolithographic;

FIG. 3 is a perspective View partially in section of the plate shown in FIG. 2 after exposure to form the image thereon; and

PEG. 4 is a perspective view partially in section of the imaged lithographie plate.

The photolithographic plate embodying the features of this invention comprises a base Sheet 10 in the form of a low cost paper base sheet having a film 12 of polyethylene bonded to the surface of the paper base sheet. The polyethylene surface is in turn provided with a coating 14 of finely divided particles of silica or colloidal silica which function as the stabilized lithographie surface 16 onto which a layer 18 of a light sensitive diazo compound is provided which reacts to form the ink receptive, water repellent image 20 on the lithographie surface lr6, upon exposure to light.

As the base sheet 10, use can be made of a metal or plastic film but, in the preparation of a low cost photolithographie plate, in accordance with the preferred practice of this invention, the base sheet 10 is formed of paper and, more preferably, a base paper which is given high Wet strength lby impregnation with resin.

The film 12 of polyethylene can be provided by coating the base sheet with a solution or emulsion of the polyethylene resin but it is preferred to laminate a film of polyethylene onto the surface of the base sheet as by extruding a thin film of polyethylene directly onto the surface of the -base sheet or by adhesively bonding a polyethylene film which has previously been formed. When formed, as by extrusion directly onto the surface of the base sheet, the polyethylene may be applied to form the laminate in coating weights of from 5 to 20 pounds per 3000 square feet of surface area and preferably about l0i3 pounds per 3000 square feet of surface area. Instead of making use of a film of polyethylene on the surface of the base sheet, other lms of plastic materials can 3 be employed, such as are formed -by coating or extrusion of polystyrene, cellulose triacetate, cellulose acetate, polyvinyl acetate and the like.

The finely divided or colloidal particles of silica `can be applied in uniform distribution over the polyethylene surface to build up a layer which may be a monomolecular coating or thicker onto the surface of the polyethylene film. To enhance the bonding relationship between the finely divided silica particles and the surface of the polyethylene film, a small amount of resinous binder may be incorporated iwith the particles of silica, such for example as emulsions of polyvinylidene chloride, polyvinyl acetate, cellulose acetate and the like. The silica particles are preferably of colloidal dimension, such as represented by an average of 15 millimicrons. They may be applied alone or they may be applied with the resinous binder, and when applied with a binder system, it is undesirable to make use of an amount of binder which is greater in parts by weight than the silica and it is preferred to make use of resinous binder in an amount which constitutes only about 5 to 20 percent by weight of the silica.

Diazo compounds suitable for use in coating onto the silica surface to produce the sensitized plate include diazo compounds or diazo resin for-ming compounds which form ink receptive reaction products in response to exposure to light. Suitable compounds are of the type described in the aforementioned Jewett et al. patent and include the reaction produ-ct of the sulfate salt of para-diazodiphenylamine with para-formaldehyde vand zinc chloride in sulphuric acid solution. It includes also the azides of diazo light sensitive resin forming compounds, polymeric azido resins, particularly aromatic azido resins or aliphatic azdo resins; diazo oxides such as described in The Aromatic Diazo Compounds, by K. H. Saunders, published 1949, by Edward Arnold & Company, London, page 29; the monomolecular imino diazides, as described on page 24 of the aforementioned Saunders publication, and paratertiary amino diazo resins. Application of the diazo compound may be effected in the manner and in the amounts described in the Jewett et al. patent for application onto the aluminum base sheet.

The following will illustrate the practice of this invention:

EXAMPLE 1 Preparation of polyethylene coated paper:

A film of polyethylene in coating weights of l pounds per 3000 square feet of surface area is extruded onto the surface of bond paper which has been vvaterproofed by about 2 percent by weight of melamine formaldehyde resin. Before treatment to coat the surface with silica, it is desirable to expose the film to corona discharge whereby the polyethylene surface is rendered more wettable.

EXAMPLE 2 Silica coating:

The polyethylene coated paper is dusted with dry colloidal particles of silica having an average size of about millimicrons to coat the surface with a thin coating of silica. The silica may be anchored onto the surface by passing the coated sheet between heated rolls.

EXAMPLE 3 Silica coating:

The polyethylene coated paper base sheet may in the alternative be coated with a composition having the following formulationl part by weight of a polyvinylidene chloride emulsion (40% by weight Solids),

1 part by weight colloidal silica (average dimension of l5 millimicrons).

The coating is applied in coating weights of about 0.25 to 4.0 pounds per 3000 square feet of surface area to provide a thin layer of the coating compositions on the polyethylene surface. The coating is then dried to set the silica as a exible layer 14 on the surface of the polyethylene 12 laminated to the base sheet 10.

4 EXAMPLE 4 Sensitizing:

The silica coated polyethylene film is then coated with a water solution containing from l to 4 percent by Weight of the light sensitive diazo resin forming material such as is formed by the reaction of 34 parts by Weight of the sulfate salt of para-diazophenylamine, 3.25 parts by Weight of para-formaldehyde and 4.5 parts by Weight of anhydrous zinc chloride and in which the mixture is introduced into parts by weight of 66 B. sulphuric acid and reacted at a temperature below 6 C. The reaction product is poured onto ice to collect a brown residue which is purified by solution in water and precipitation with a saturated solution of zinc chloride to produce a yellow precipitate as the end product.

The reaction and coating are carried out under subdued light and the solution of the diazo resin forming compound is applied to provide a coating Weight of about 0.001 to 0.003 or more grams per square foot of surface area.

In use, the sensitized plate is exposed to a negative transparency prepared from an original by usual photographictechnique. The diazo in the exposed portions is converted to an ink receptive imaging material 20 while the diazo in the non-exposed portions of the plate refV mains soluble for removal by the repellent or other aqueous uid used to treat the plate for development after exposure. y

The imaged plate can be mounted on a lithographie press for the usuual sequence of wetting the plate with water repellent and inking the plate whereby the nonimaged portions of the plate are wet with water While the ink is repelled by the wetted non-imaged portions of the plate and received by the unwet imaged portions of the plate for subsequent transfer of ink from the plate to an offset blanket and from the blanket to the copy sheet, in accordance with conventional lithographie procedures.

It will be apparent from the foregoing that I have provided a new and improved photolithographic or light sensitive lithographie plate which can be imaged from an original to .produce an imaged photolithographic plate from which multiple copies can be reproduced.

It will be understood that changes may be made in the details of formulation, methods of application and in the construction of the plate, without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A light sensitive photolithographic pvinting plate comprising a paper lbase sheet, a thin polyethylene layer on the surface of the base sheet, a coating consisting of colloidal silica on the surface of the polyethylene layer to provide a stabilized, ink repellent, water receptive lithographic surface and a coating of a light sensitive diazo resin forming compound on the stabilized lithographie surface.

2. A photolithographic plate as claimed in claim 1 in which the polyethylene is in the form of a film laminated onto the surface of the base sheet.

3. A photolithographic plate as claimed in claim 1 in which the silica particles are of an average dimens-ion of about 15 millimicrons.

References Cited UNITED STATES PATENTS 3,062,648 11/ 1962 Crawford 96-33 3,037,862 6/ 1962 Neth 96-75 FOREIGN PATENTS 886,652 1/ 1962 Great Britain.

NORMAN G. TORCHIN, Primary Examiner.

R. E. MARTIN, Assistant Examiner. 

1. A LIGHT SENSITIVE PHOTOLITHOGRAPHIC PRINTING PLATE COMPRISING A PAPER BASE SHEET, A THIN POLYETHYLENE LAYER ON THE SURFACE OF THE BASE SHEET, A COATING CONSISTING OF COLLOIDAL SILICA ON THE SURFACE OF THE POLYETHYLENE LAYER TO PROVIDE A STABILIZED, INK REPELLENT, WATER RECEPTIVE LITHOGRAPHIC SURFACE AND A COATING OF A LIGHT SENSITIVE DIAZO RESIN FORMING COMPOUND ON THE STABILIZED LITHOGRAPHIC SURFACE. 